This invention relates generally to refrigeration and operation and more particularly to a method and apparatus for boosting the cooling capacity and efficiency of air-conditioning systems under a wide range of ambient atmospheric conditions.
In air conditioning, the basic circuit is essentially the same as in refrigeration. It comprises an evaporator, a condenser, an expansion valve, and a compressor. This however, is where the similarity ends. The evaporator and condenser of an air conditioner will generally have less surface area. The temperature difference .DELTA.T between condensing temperature and ambient temperature is usually 27.degree. F. with a 105.degree. F. minimum condensing temperature, while in refrigeration the difference DT can be from 8.degree. F. to 15.degree. F. with an 86.degree. F. minimum condensing temperature.
I have previously improved the cooling capacity and efficiency of refrigeration systems. As disclosed in my U.S. Pat. No. 4,599,873, this is accomplished by addition of a liquid pump at the outlet of the receiver or condenser. Operation of the pump adds 5-12 p.s.i. of pressure to the condensed refrigerant flowing into the expansion valve, a process I call liquid pressure amplification. This suppresses flash gas and assures a uniform flow of liquid refrigerant to the expansion valve, substantially increasing cooling capacity and efficiency. The best results are obtained when such a system is operated with the condenser at moderate ambient temperatures, usually under 80.degree. F. As ambient temperatures rise above the minimum condensing temperature, the advantages gradually decrease. The same thing happens when the principles of my prior invention are applied to air conditioning, except that the minimum condensing temperature is higher.
While conventional air-conditioning systems can benefit from my prior invention, the greatest need for air conditioning is when ambient temperatures are high, over 80.degree. F. Conventional air conditioning becomes less effective and efficient as ambient temperatures rise to 100.degree. F. or more, as does use of my prior liquid refrigerant pressure amplification technique.
In conventional air conditioning systems, as liquid refrigerant exits the thermal expansion valve, a certain portion of it will flash or boil off to reach the desired coil temperature. This flashing off of liquid refrigerant does no practical refrigerant work yet the compressor must compress this vapor which increases the power requirement of the system. Thus, it is desirable to decrease system flashing and therefore increase the efficiency of air conditioning systems.
One of the important functions of an air conditioning system is dehumidification. Dehumidification has many advantages. Lower humidity reduces the amount of compressor power needed. Lower relative humidity also allows a higher thermostat set point while providing for the same level of human comfort. This translates into an energy savings of about 3% to 5% per .degree. F. In office buildings, apartments, hotels, and homes, lower humidity in delivery ducts reduces mold, bacteria growth, allergic reactions, and building sickness syndrome.
Lower humidity is also very advantageous to grocery stores. For example, excessive humidity greatly increases grocery store refrigeration costs. It reduces heat transfer and thus requires lower coil temperatures, requires more frequent defrosting, and can damage product appearance.
Dehumidification is accomplished by decreasing the relative humidity of the flow of ambient air received by the air conditioning system. Relative humidity can be decreased in two ways: (1) removing moisture from the air; and (2) heating the air to increase its volume while maintaining a constant amount of water contained therein.
In many areas, moisture removal is the most important function of an air conditioning system. In addition, moisture removal generally consumes much of the power required to operate the system. It is the system's evaporator that removes most of the moisture from ambient air in an air-conditioning system. Thus, the system will remove more moisture if the efficiency of the evaporator is increased.
The second method of dehumidification is reheating ambient air to increase its relative humidity. Thus, if both moisture removal and reheating could be accomplished simultaneously in a single system, greater dehumidification would be achieved and the efficiency of the air conditioning system would be greatly enhanced. Moreover, decreased flashing would require less compressor work and thus gives a further increase in efficiency. Accordingly, it is the object of this invention to provide such a system.